The invention relates to a current supply apparatus for a synchronous machine, and, more particularly, to such apparatus including means for supplying current to at least two power windings of the machine and including switching means for changing the polarity of the current that is applied to the power windings.
It is known in the art to supply current of periodically changing polarity to the windings of a synchronous machine to operate the machine. For example, in the U.S. Pat. No. 3,995,203, at FIG. 7 there is shown a reluctance machine having first and second power windings that are supplied with driving current from a current source. Each of the windings has a center tap and the center taps are connected by means of an excitation winding. The ends of the first power winding are connected to one terminal of the current source through respective thyristors. Likewise, the ends of the other power winding are connected to the second terminal of the current source through additional respective thyristors.
In this prior art power supply system, two thyristors must operate simultaneously to conduct supply current to the power windings. In addition, since the supply current must always pass through two series-connected thyristors, there is an appreciable voltage drop that is particularly noticable at low operating voltages. Furthermore, since each of the thyristors must conduct to carry current during half of a power supply cycle, the power handling capacity of the thyristors must be relatively large.
There are significant losses in such a prior art system, particularly at low operating voltages, and the losses cause an appreciable deterioration in the total operational efficiency of the power supply apparatus of the system.
Accordingly, it is an object of the invention to provide a simple and effective means to apply current of changing polarity to the power windings of a synchronous machine in a system having lower losses and, therefore, greater efficiency.
A further object of the invention is to provide such a current supply system wherein thyristors having a lower rated current capacity may be used.
Another object of the invention is to provide a current supply apparatus wherein only one controllable switching means is operable at a time to conduct current to the power windings of the synchronous machine, thereby reducing the voltage drop associated with such apparatus by one-half.
A further object of the invention is to provide a current supply apparatus for a synchronous machine wherein each switching thyristor of the apparatus carries current only during one-fourth of a power supply cycle so that thyristors having lower rated current carrying capacities may be used.
These and other objects of this invention will become apparent from a review of the detailed specification which follows and a consideration of the accompanying drawings.